Strong or weak? What controls magnetic anomalies in the Admiralty igneous complex, northern Victoria Land, Antarctica

The Devonian-Carboniferous Admiralty igneous complex (i.e. Admiralty plutonites and Gallipoli volcanics) of northern Victoria Land, Antarctica, forms part of a widespread magmatic system comprising felsic volcanic, subvolcanic and plutonic lithologies. Due to extensive snow and ice coverage, aeromagnetic data has been used to interpret the extent of igneous bodies where surface exposure of igneous rocks is limited. However, some exposures generate strong positive magnetic anomalies, while others produce weak or negligible responses, raising questions about the factors controlling magnetic susceptibility and interpretation of aeromagnetic data where exposure is absent.

We focus on several key locations with exposed Admiralty igneous rocks showing strong positive anomalies (Everett, Salamander and southern Alamein ranges, Mariner Plateau), negligible anomalies (Tucker Glacier region), and a combination of weak and strong anomalies (Yule Bay) to explore how variations in rock properties and geochemical composition relate to observed magnetic anomalies.

Combining aeromagnetic surveys and in-situ susceptibility measurements with detailed petrology, modal mineralogy, whole-rock geochemistry (major, minor, and trace elements) and ongoing age dating allows a better understanding of the causes of low versus high magnetic anomalies in rocks previously ascribed to a single magmatic event. In particular we are testing whether (a) multiple, compositionally distinct magmatic pulses, (b) variable degrees of alteration, and/or (c) different levels of exposure can account for the observed discrepancies in magnetic anomalies.

Magnetic and susceptibility data, when combined with petrological and geochemical analyses, provide a powerful tool to investigate the origin of variations in magnetic susceptibility, particularly in regions with limited outcrops.